Environmental Engineering Reference
In-Depth Information
Coefficients of lateral earth pressure
is the term often used to refer to
K
p
and
K
a
. When rup-
ture occurs along some failure surface, earth pressures are mobilized. The magnitudes of
the pressures are a function of the weight of the mass in the failure zone and the strength
acting along the failure surface. These pressures (
P
p
or
P
a
) are often expressed in terms of
the product of the weight of the mass times the active or passive coefficients, as follows:
P
p
K
p
γ
z
(3.40)
P
a
K
a
γ
z
(3.41)
3.4.3
Rock Strength Measurements
General
Intact Rock
The confined strength of fresh, intact rock is seldom of concern in practice because of the
relatively low stress levels imposed.
Brittle shear failure occurs under very high applied loads and moderate to high confin-
ing pressures, except for the softer rocks such as halite, foliated and schistose rocks, and
lightly cemented sandstones. In softer rocks, rupture occurs in a manner similar to that in
soils, and the parameters described in
Section 3.4.2
hold.
Under very high confining pressures (approximately 45,000 psi or 3000 bar), some com-
petent rocks behave ductilely and failure may be attributed to plastic shear (Murphy,
Active wedge
Compression
Tension
W
Passive zone
−
P
a
Cracks
Passive
wedge
Failure
surface
Failure
surface
+
+
Active zone
P
p
R
(a)
(b)
Q
F
F
p
Active
zone
W
1
P
p
Passive
zone
P
a
Prandtl zone
W
2
P
p
R
(c)
(d)
(e)
FIGURE 3.36
Examples of the occurrence of active and passive pressures encountered in practice: (a) slope; (b) retaining
wall; (c) anchored bulkhead; (d) anchor block; (e) foundation.
